1. Field of the Invention
This invention relates to an apparatus for controlling a continuously variable transmission (hereinafter referred to as "CVT") used for a transmission of an engine power.
2. Description of the Prior Art
In U.S. patent Ser. No. 4,595,916 corresponding to Japanese Patent Application No. 58-17550, the assignee of the present application disclosed a CVT controlling apparatus which sets a desired engine speed in a transient running condition of a vehicle, which is different from a desired engine speed used in a steady running state of the vehicles. According to that controlling apparatus, when an intake throttle position .theta. is abruptly changed, a desired steady-state engine speed No is held at a desired engine speed Ns before the change in .theta., for a predetermined time Ta after the commencement of that change and is changed in steps by an amount equal to a product B.multidot..DELTA.Ns of a difference .DELTA.Ns between the desired steady-state engine speeds Ns before and after the change in .theta., and a constant B (provided 0&lt;B&lt;1) after the predetermined time Ta has elapsed. This is intended to improve the response of the engine. Thereafter the desired engine speed No is gradually changed toward the steady-state engine speed which corresponds to the newly established throttle position Ns after the change in .theta..
The predetermined time Ta is provided to confirm whether or not a driver's intention or request for acceleration or deceleration of the vehicle is true. However, an inconvenience is encountered since the presence of the predetermined time Ta gives an impression of delayed acceleration to the driven when an abrupt acceleration requiring a kick-down of the transmission is desired by the driver. Also, when the driver depresses an accelerator pedal for a time more than the predetermined time Ta, the stepping change in No may be less than an optimum value, causing insufficient initial acceleration of the vehicle.
On the other hand, in U.S. patent Ser. No. 918,058 filed Oct. 14, 1986, which is a continuation-in-part application of parent application Ser. No. 661,813 filed Oct. 17, 1984, claiming the priority of Japanese Patent Application No. 58-194191 filed by the assignee, there is shown a control apparatus wherein the desired engine speed No is abruptly changed, at time intervals of .DELTA.t [.DELTA.t is a time necessary for converting an analog output of a throttle position sensor to digital value with an A/D (analog/digital) converter or a multiple] of that time, for a first time span following the predetermined time Ta (including Ta=0). After the passage of the first time No span, the desired engine speed is gently changed toward Ns corresponding to the newly established throttle position .theta.. In this case, the variation .DELTA.No in No for the unit time .DELTA.t within the first time span is a product B.multidot..DELTA.Nr of a reference value .DELTA.Nr and said constant B. The difference between Ns before and after .DELTA.t, the difference between the present Ns and No before .DELTA.t, or the difference between the present Ns and the actual engine speed Ne are selected as the reference value .DELTA.Nr. However, since the constant B is preset to a value adapted to a variation .DELTA..theta. in .theta. before and after the change in .theta., the desired engine speed No within the first time span is disadvantageously gradually deviated from an optimum value.